Study On Modification And Oil/Water Separation Performance Of PTFE Flate Membrane

The oil water mixture is widely distributed in petrochemical,semiconductor processing and other fields,causing serious pollution to the environment;in addition,the existence of moisture in the refined oil can cause damage to the equipment.Membrane separation technology has been a hot topic in the field of separation of oil-water mixtures,especially in the field of separation membrane materials.Polytetrafluoroethylene(PTFE)flate membrane is a promising oil-water separation material due to its excellent chemical stability,corrosion resistance,mechanical strength and separation efficiency.In this paper,field emission scanning electron microscopy(SEM),aperture analyzer,video contact angle meter,water flux tester and UV-visible spectrophotometer were used to study the effect of the membrane structure and pore size,hydrophilic property and wettability on oil water separation performance.The main research contents and results are as follows:(1)Utilizing the oleophilic property of the PTFE flate membrane,it was used as a"water-removing type"material to separate a small amount of water in the sewing machine oil.The effect of the membrane structure and the separation temperature on the separation performance was studied.The results showed that with the increase of the pore size and separation temperature of the PTFE flate membrane,the permeation flux of the oil-water mixture was increased,and the separation efficiency was reduced.According to the video contact angle meter,the surface water contact angle can be as high as 130.19°,and the oil contact angle was less than 60°.According to the oil-water separation experiment,when temperature was 25°C and the pore size was 0.2109μm,the PTFE flate membrane had the best performance of the oil-water separation,the permeation flux of the sewing machine oil was 30.14 Kg/(m~2·h),and the water separation efficiency was98.34%.(2)Hydrophilic PTFE flate membrane was prepared by hydrophilic modification of PTFE flate membrane by immersion and rolling process.It was as a“oil removing type”material to separate a small amount of oil contained in water.The effects of concentration of hydrophilic agent and pore size of flate membrane on the separation performance,wettability and permeability of water were studied,and the hydrophilic stability and reusability of the hydrophilic agent were investigated.The results showed that there were obvious hydrophilic particles on the fibrils and nodes of the PTFE flate membrane by scanning electron microscope(SEM)analysis.The increase of concentration of hydrophilic agent can improve the wettability and permeability of water and the permeation flux and separation efficiency of oil-water mixture.The increase of pore size of PTFE flate membrane can improve the permeability of oil/water mixture,but decrease the separation efficiency.By controlling the pore size of the PTFE flate membrane and the concentration of the hydrophilic agent,the preparation conditions with the best oil-water separation performance were obtained:the pore size of the PTFE flate membrane was 0.2109μm,and the concentration of the hydrophilic agent was 2.5 wt%.At this time,the surface contact angle of the hydrophilic PTFE flate membrane was 71.67°,the permeate flux of pure water was 4423.4Kg/(m~2·h),and the permeation flux of the oil water mixture was 620.48 Kg/(m~2·h).The separation efficiency of the oil was 57.68%;its hydrophilic stability was also good.When soaked for 10 h under strong acid conditions,the water flux was only reduced by 3.2%;when soaked for 10 h under strong alkaline conditions,the water flux was reduced by 8.3%.However,its anti-pollution performance was poor,and the flux recovery rate was only 7%.(3)In order to improve the anti-pollution performance of the hydrophilic PTFE flate membrane,hydrophilic and oleophobic PTFE flate membrane was prepared by immersion and rolling process,which hydrophilic agent and oleophobic agent were used for surface treatment.PTFE flate membrane.It was used as“oil-removing type”material for the separation of oil water mixture.The effects of the concentration of the hydrophobic agent,the modification sequence and the separation pressure on the oil-water separation performance were studied,and the hydrophilic stability and reusability of the oleophobic agent were also investigated.The results showed that the increase of the concentration of oleophobic agent was beneficial to increase the oil-water separation efficiency and reusability of the membrane,but also to reduce the water permeability and wettability.When the PTFE flate membrane was first modified by 3.0 wt%oleophobic agent,then by 2.5 wt%hydrophilic agent,and the separation pressure was 0.04 MPa,it had the best performance of oil water separation.Its water contact angle(WCA)was 85.52°,permeation flux of pure water was 2668.5 Kg/(m~2·h);hydrophilic stability was good,after soaked for 10 h under strong acid conditions,water flux only drops by 2.5%;after soaked for 10 h under strong alkaline conditions,the water flux only decreased by 8.1%;after soaked in deionized water for 10 h,the water flux decreased by only 0.3%.At this time,the separation efficiency of the oil-in-water emulsion was 86.1%,and the permeation flux of oil water mixture was 109.97 Kg/(m~2·h);and its anti-pollution performance was good,the flux recovery rate was 91%.